FTM help

FTM. My baby girl is 3 weeks old, she was 4 weeks early. She's formula feed at the moment but id like to try breastfeeding I tried in the beginning but it was to uncomfortable, i have never put my baby to my breast yet.. Would she latch right I also dont know how she should latch. Ive tried pumping it was painful I was able to get some of my colostrum (I think thats the word) out but havent tried since..

Is it too late to try again?

I put baby girl to my nipple and she latched on properly but how to i know if milk is coming out for her she is sucking and looks like swallowing but I'm not sure.. I just dont know if milk is coming out of my nipple into her mouth how am i supposed to know?